Download Purpose: To compare ecological succession in a variey of biomes

Science 7
Technical Reading
You Call This Success?
EQ: Why should I be concerned if
rainforests are destroyed?
Targeted Skills
Thinking and Reasoning
 Problem Solving/Decision Making
 identify relevant factors
Enduring Understandings
Equilibrium within systems is regulated by the interactions of
biotic and abiotic factors.
Concepts Important to Know and Understand
relationship of structure and function, human impact,
environmental responses
Broad Brush Knowledge
carbon and nitrogen cycles, temperature, deforestation
Core Objectives
8. Analyze how (eco) systems maintain equilibrium.
10. Describe the interactions that occur among abiotic and biotic
factors, including humans, within ecosystems.
Purpose: To compare ecological succession in a variey of biomes.
Procedure: After reading the passage about succession in different biomes, read and answer the
questions about environmental change.
Imagine a beautiful Saturday morning.
Instead of sleeping late or hanging out with
your friends, your mom insists that you weed
the flowerbed. You unhappily pull on a pair of
gloves, grab a bag, and get to work. Just
before the door slams behind you,
you hear your mother’s voice, “You
know, Sweetie, there wouldn’t be
weeds to pull if you’d covered the
flower bed with a layer of mulch
like I asked you to!”
Environments, whether as small as a yard or as
large as a forest, can be disturbed or damaged
in a variety of ways. Disturbances can be huge
naturally occurring events like a volcanic
eruption, forest fire, or flood. Disturbances
can also be manmade events like building a
road, digging a new flowerbed, or damming a
river. When snorkeling, people are asked not
to stand on or touch the coral.
Even a
footstep can be an environmental disturbance
Updated Klein ISD, 2008
in a fragile ecosystem. The on-going process of
environmental change is called succession.
Ecologists
evaluate
an
environmental
disturbance by asking several questions:

Severity: Were all the trees removed as
in slash and burn agriculture or were
trees selectively harvested?

Size: Did the flood or fire consume 1 or
100 hectares of land?

Frequency: Do similar disturbances
happen often?

Timing: Did the disturbance happen
during the height of the rainy season or
during the dry season when creatures are
more stressed?
An
additional
measure
of
environmental
damage
is
determining how quickly plants and
animals return to the area. If a
disturbance occurs because of
natural causes, such as fire after a lightning
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strike, or flooding of an unchanged creek, it is
assumed that this type of disturbance happens
fairly regularly. The creatures in the area are
likely to have behavioral adaptations that allow
them to survive.
In most forest ecosystems, small fires happen
frequently. This process returns carbon and
other nutrients to the soil. Following such a
fire, buried seeds that were protected from
the heat begin to sprout. In
fact, there are some seeds,
such as the jackpine, that
rely on the heat of a fire in
order to germinate. These young seedlings
attract animals and insects. However, fires
that destroy large areas cause great changes
to forest ecosystems. After the fire, the soil
is unprotected and is easily washed away by
rain. In rainforests, the soil is baked by the
intense sunlight and becomes brick-like. Seeds
that were buried or were blown into the area
by the wind cannot take root. The ground
remains bare.
The succession or change of the environment
over time happens in a predictable pattern.
Plants and animals tend to return from the
edges, slowly moving from less disturbed areas
into the center. The first plants that thrive
following a major disturbance are pioneer or
colonizing species. These small plants, such as
lichens and moss begin to break down the
exposed rock and prevent soil from washing
away. In general, these species grow rapidly
and quickly produce offspring.
Following a minor disturbance, opportunistic
species, such as grasses and
plants with soft green stems,
Updated Klein ISD, 2008
follow. There may be hundreds or thousands of
seeds in one square meter of healthy soil
waiting for the right conditions to sprout.
Although these opportunistic plants are often
thought of as weeds, they are important to the
health of the ecosystem because they keep
the soil in place and provide moisture to the
soil. Insects in the area will often eat these
small plants rather than young trees. At this
point in succession, there is typically the
greatest variety of plant and animal species.
The final stage of succession is called a climax
community. In a forest community, the trees
are mature and are the major vegetation.
Climax communities are stable, but vary from
biome to biome. The vegetation of a climax
community can live for many years and create
shelter and food for many
species of animals. Since
little light reaches the
forest floor, there are fewer species of plants
found here.
In rainforest ecosystems, a small disturbance
such as a tree falling increases the amount of
light that reaches the forest floor. This
additional sunlight causes plants to grow
quickly. Bushes and vines fill in the void of the
fallen tree.
However, more severe
disturbances
may
permanently
change
rainforest communities. In many areas, since
the rainforest soil is so poor, repeated clearing
of the forest will lead to severe soil depletion,
and the normal patterns of succession will no
longer
occur.
Instead
of
returning to forest, the area will
become a grassy area because
there aren't enough nutrients
remaining in the soil to support
trees. Succession is continuous
competition
for
limited
resources.
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Consider the following scenarios:
The year is 1899. You are a Swedish immigrant who has bought a small farm in southeastern
Nebraska. You spend your first year as a farmer chopping down the maple and oak trees and clearing
the small bushes from a 10-acre plot of land. For the next thirty years, you grow corn on the 10-acre
field. In 1929, you retire, move to town, and no longer plow the field and plant corn each spring. To
celebrate your 101st birthday, your grandchildren bring you back to farm to reminisce.
1. What has happened to the 10-acre field?
2. What would have to be done if your great-grandchildren wanted to plant corn in this field?
3. Where are the tallest trees?
4. Why would there be more varieties of plants and animals in the center of the field?
The year is 2000. You are a middle school student who has been asked to dig a new flowerbed in the
backyard of your home. It is late July and the temperature has hovered around 100 F for the past
two weeks. You dig out the grass, place bricks around the edge for a border and arrange plants from
a local nursery according to your parents’ instructions. The next spring, your mother sends you out
to weed the flowerbed.
5. Where did the weeds come from?
6. You notice grass has also grown into the flowerbed. Where is the grass thickest?
7. What would likely happen to the flowerbed if it were not weeded regularly?
8. Why didn’t the weeds emerge during the summer you planted the flowerbed?
9. How would covering the bare ground with mulch prevent the growth of weeds?
Interpretation:
What factors are unique to rainforests that affect succession?
Updated Klein ISD, 2008
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